Diesel engine operation involves combustion that generates exhaust gas. During combustion, air is delivered through an intake valve to cylinders and fuel is injected into the cylinders forming an air/fuel mixture. The air/fuel mixture is combusted therein. Air flow delivered to the cylinders can be measured using a mass air flow (MAF) sensor. The MAF sensor measures the total intake of fresh air flow through an air induction system. After combustion, a piston forces exhaust gas in the cylinders into an exhaust system. The exhaust gas may contain various emission components including diesel particulates or soot.
Engine systems often include an exhaust gas recirculation (EGR) system to reduce engine emissions and combustion noise as well as to improve fuel economy. EGR involves re-circulating exhaust gases back into the cylinders, which reduces the amount of oxygen available for combustion and lowers cylinder temperatures. For exhaust gas to flow into the intake manifold, exhaust pressure must be greater than the intake manifold pressure (i.e. a boost condition). An EGR system enables ignition timing to remain at an optimum point, which improves fuel economy and/or performance.
Advanced combustion approaches, such as premixed charge compression ignition (PCCI), used to reduce emissions require large levels of EGR. Currently EGR rates are estimated from the change in air flow that occurs when an EGR valve is actuated. This method of EGR rate estimation is accurate during steady state operation. The accuracy of estimation tends to deteriorate during transient operation.
Transitioning between various load-speed conditions and the various levels of EGR during transient maneuvers can result in high emissions, noise levels, and fuel consumption. Additionally, current approaches of estimating the EGR level are dependent on calibrations conducted when the air and EGR passages are clean. These estimations are inaccurate when the EGR system becomes blocked (e.g. EGR cooler fouling).